moverandom(creature[green]) from(mygraveyard) to(opponentbattlefield)
example card
[card]
name=Tariel, Reckoner of Souls
auto={t}:moverandom(creature) from(opponentgraveyard) to(mybattlefield)
mana={4}{W}{B}{R}
abilities=Flying,vigilance
type=Legendary Creature
subtype=Angel
power=4
toughness=7
text=Flying, vigilance {T}: Choose a creature card at random from target opponent's graveyard. Put that card onto the battlefield under your control.
[/card]